Needle unit with floating needle hub

ABSTRACT

The present invention provides a needle unit ( 10 ) for use with a pen injection device, wherein the needle unit ( 10 ) comprises a needle shield ( 50 ) and an axially movable needle hub ( 25 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.17/265,827, filed Feb. 4, 2021, which is a 35 U.S.C. § 371 NationalStage application of International Application PCT/EP2019/071467(published as WO 2020/030798), filed Aug. 9, 2019, which claims priorityto European Patent Application 18188538.5, filed Aug. 10, 2018; thecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to medical devices and moreparticularly to needle units for use with drug delivery devices.

BACKGROUND OF THE INVENTION

Many drugs must be administered parenterally to be effective in the bodyand some of these, e.g. insulin and glp-1, may require one or more dosesto be delivered subcutaneously on a daily basis. Subcutaneous drugdelivery is often associated with discomfort as many people dislike thethought of having an injection needle inserted through the skin. Anundisclosed number of people even suffer from needle-phobia, and thesepeople often benefit from using needle units with shielded needles,where the injection needle remains out of sight during handling of theneedle unit, including insertion of the injection needle into the skin.

Typically, this type of needle unit comprises an axially movable sheathwhich can be slid between a first position in which it covers theinjection needle and a second position in which the injection needle isexposed and ready for injection. In some cases the sheath is springloaded such that it is automatically slid back to the first positionwhen the injection needle is retracted from the skin. An example of thisis disclosed in US 2003/0078546 (Jensen).

Needle units are typically wrapped and sealed individually to ensuresterility prior to use. In connection with a dose administration actionthe user must therefore unwrap the needle unit, mount it on theinjection device, perform the injection, dismount it from the injectiondevice, re-wrap or otherwise encapsulate it to prevent needle stickinjuries, and finally dispose of it, preferably in a dedicated sharpscontainer.

The readying and subsequent removal of the needle unit is both the mostcomplicated and the most time-consuming part of the injection procedure.Especially for young and elderly users the handling of the small itemsand foils can present a challenge and make the task of injection a bitcumbersome. As a result, some users reuse the needle unit several times.In fact, some users only change the needle unit when the injectiondevice is empty, or if the needle for example exhibits clogging orhooking. This reduces the number of times these users have to carry outneedle handling activities significantly.

However, it also entails increased risks of both infections and needlestick injuries, the former due to needle contamination and the latterdue to the users typically disposing of the original needle unitpackaging in connection with the fitting of the needle, why thispackaging is not available as receptacle when they change the needleunit after several times of reuse.

WO 2015/062845 (Novo Nordisk A/S) discloses a needle unit for a peninjection device where a portion of the front needle is housed betweeninjections in a reservoir holding a preservative containing liquid. Thisportion of the front needle is thus cleaned by, and stored in, thepreservative containing liquid following each injection action, therebyreducing the risk of microbial contamination. The preservativecontaining liquid is identical to the drug present in the cartridge andis transferred from the cartridge to the reservoir in connection with afirst use of the injection device.

In both of the above types of needle units the injection needle ishidden by a shield with a seal and only protrudes the seal duringinsertion into the skin. This reduces the user's awareness of thepointed needle which tends to lead to a reduced sensation of pain.However, it also prevents the user from verifying that the needle tip isactually properly inserted. With such needle units there is a risk thatthe skin portion around the injection site, during displacement of theneedle shield, deflects and forms a cavity in which the needle tip canrest without penetrating the epidermis. This will lead to a so-calledwet-shot, where the dose of drug is undesirably expelled onto thesurface of the skin instead of into the body.

SUMMARY OF THE INVENTION

It is an object of the invention to eliminate or reduce at least onedrawback of the prior art, or to provide a useful alternative to priorart solutions.

In particular, it is an object of the invention to provide a needle unitwhere the injection needle remains out of sight both during an injectionand between injections, yet where proper injection needle insertion isensured.

It is another object of the invention to provide such a needle unitwhich is simple, easy to operate, and which requires few handling steps.

It is a further object of the invention to provide an injection systememploying such a needle unit.

In the disclosure of the present invention, aspects and embodiments willbe described which will address one or more of the above objects and/orwhich will address objects apparent from the following text.

In one aspect the invention provides a needle unit according to claim 1.

Accordingly, a needle unit for use with a pen injection device isprovided. The needle unit comprises a base member adapted to be attachedto, e.g. mounted on, a needle mount of the pen injection device. Thebase member extends along a longitudinal axis and comprises aninteriorly arranged attachment portion which defines a proximalreceiving space and which is configured for reception and retention ofthe needle mount.

The needle unit further comprises a needle hub, which is coupled withthe base member distally of the interior attachment portion, aninjection needle which is fixedly mounted in the needle hub and whichcomprises a distal needle end portion intended for insertion through askin barrier, and a proximal needle end portion extending into theproximal receiving space for permanent residence therein, and a needleshield arranged exteriorly of the needle hub. The needle shieldcomprises an axially extending wall and is axially displaceable relativeto the base member between an extended position and an intermediateposition and further between the intermediate position and a maximumdisplaced position. A first bias structure biases the needle shieldtowards the extended position.

The needle hub is axially reciprocatable relative to the base memberbetween a proximal needle hub position and a distal needle hub position.A second bias structure, acting between the base member and the needlehub, biases the needle hub towards the distal needle hub position.

During axial displacement from the extended position to the intermediateposition the needle shield undergoes relative motion with respect to theneedle hub from a needle covering relative position in which the distalneedle end portion is surrounded by the axially extending wall to aneedle exposing relative position in which the distal needle end portionextends distally beyond the axially extending wall. During axialdisplacement from the intermediate position to the maximum displacedposition the needle shield undergoes joint motion with the needle hubwhich brings the needle hub from the distal needle hub position to theproximal needle hub position. Said joint motion may for example be dueto a contact between the needle shield and the needle hub, e.g. a distalsurface of the needle hub, established in the intermediate position.

The degree of exposure of the injection needle is thus determined by therelative axial position of the needle hub and the needle shield. Inconventional prior art needle units the distal needle end portion isfully exposed only when the needle shield is fully displaced, or when itis not possible in practice to displace the needle shield further.However, in the present needle unit construction, where the needle hubis arranged floatingly in the base member, the distal needle end portionis fully exposed before the needle shield is fully displaced, and toobtain full needle shield displacement a user needs to overcome anadditional force from the second bias structure. The user is thusencouraged to increase the pressure and cause further displacement ofthe needle shield in an effort to reach an apparent desired end state ofthe needle insertion, at a point where the distal needle end portion isalready fully exposed.

Hence, the user actually uses more than adequate force in order toaccomplish the needle insertion, and the additional force applied to theinjection pen together with the additional travel of the needle shield,performed jointly with the needle hub, provides for an increased contactpressure between the needle unit and the skin surface, which eliminatesthe risk of cavity formation and results in a proper positioning of thedistal needle end portion within the skin.

The needle shield may comprise an interior chamber structure holding anantibacterial substance, and the distal needle end portion may reside inthe antibacterial substance when the needle shield is in the extendedposition. The distal needle end portion is thereby cleaned after aninjection and maintained in a biostatic environment between injections,allowing for safe multiple reuse of the needle unit with an ensuingreduction of needle unit disposals.

In some embodiments of the invention the antibacterial substancecomprises an antibacterial rubber plug which the distal needle end isthen ejected from during injection procedures and retracted back intoafter completed injection.

In other embodiments of the invention the antibacterial substancecomprises a preservative containing liquid drug, e.g. identical to theone held by the pen injection device.

The pen injection device may be adapted to hold a drug reservoir of thecartridge type having a penetrable self-sealing septum. The penetrableself-sealing septum is then positioned at a distal end portion of theneedle mount such that when the base member is mounted over the needlemount the proximal needle end portion in the proximal receiving spacetranspierces the penetrable self-sealing septum to establish fluidcommunication with an interior of the drug reservoir. Because theproximal needle end portion is positioned in the proximal receivingspace both when the needle hub is in the proximal needle hub positionand in the distal needle hub position the fluid communication betweenthe interior of the drug reservoir and the injection needle remainsuninterrupted even if the needle unit is reused. The penetrableself-sealing septum does therefore not need be repeatedly penetrated inconnection with multiple reuses of the needle unit. It is desirable toavoid multiple penetrations of such a septum because at each penetrationthere is a risk that coring of the septum will occur. Furthermore, ifthe interior of the drug reservoir is filled, or substantially filled,with a preservative containing liquid drug the uninterrupted fluidcommunication will ensure establishment of a bacteria hostile internalenvironment positively contributing to keeping the needle interiorclean.

The first bias structure may comprise a first compression spring, actingbetween the base member and the needle shield. The second bias structuremay comprise a second compression spring. The user must then overcomefirstly the biasing force from the first compression spring to effectthe displacement of the needle shield from the extended position to theintermediate position, in which the distal needle end portion is fullyexposed, and secondly the combined biasing force from the firstcompression spring and the second compression spring to obtain a fullneedle shield displacement.

An exterior surface portion of the needle hub may comprise alongitudinal hub track, and the base member may further comprise aninner section carrying a radially inwardly directed inner sectionprotrusion adapted to travel the longitudinal hub track between aproximal hub track end and a distal hub track end, a position of theradially inwardly directed inner section protrusion at the proximal hubtrack end defining the distal needle hub position, and a position of theradially inwardly directed inner section protrusion at the distal hubtrack end defining the proximal needle hub position. This provides for avery simple construction where the possible movements of the floatingneedle hub relative to the base member are well-defined.

An exterior surface portion of the needle shield may comprise alongitudinal shield track, and the base member may further comprise anouter section carrying a radially inwardly directed outer sectionprotrusion adapted to travel the longitudinal shield track between aproximal shield track end and a distal shield track end, a position ofthe radially inwardly directed outer section protrusion at the proximalshield track end defining the extended position, and a position of theradially inwardly directed outer section protrusion at the distal shieldtrack end defining the maximum displaced position. Similarly to theabove, this provides for a very simple way of defining the possiblemovements of the needle shield relative to the base member.

The interior attachment portion may form part of the inner section, andthe inner section may further comprise a transversal partition adjacenta distal end section of the interior attachment portion, the transversalpartition comprising a through-going bore for slidable reception of theinjection needle. This establishes a well-defined axial position of theneedle mount relative to the base member following attachment of theneedle unit on the pen injection device and thereby provides for apredetermined axial position of a drug reservoir carried by the peninjection device relative to the proximal needle end portion, allowingan optimised and uniformised extent of protrusion of proximal needle endportions into respective drug reservoirs, relevant for minimising drugresiduals in the various drug reservoirs.

In another aspect the invention provides an injection system comprisinga needle unit as described in the above and a pen injection devicecomprising a needle mount. The needle mount and the interior attachmentportion may be configured for releasable interengagement, e.g. in casethe pen injection device is of the durable device type, or may bepermanently engaged, e.g. in case the pen injection device is of theprefilled disposable device type. In case of the latter the lifetime ofthe needle unit equals the lifetime of the pen injection device.

In the present specification, reference to a certain aspect or a certainembodiment (e.g. “an aspect”, “a first aspect”, “one embodiment”, “anexemplary embodiment”, or the like) signifies that a particular feature,structure, or characteristic described in connection with the respectiveaspect or embodiment is included in, or inherent of, at least that oneaspect or embodiment of the invention, but not necessarily in/of allaspects or embodiments of the invention. It is emphasized, however, thatany combination of the various features, structures and/orcharacteristics described in relation to the invention is encompassed bythe invention unless expressly stated herein or clearly contradicted bycontext.

The use of any and all examples, or exemplary language (e.g., such as,etc.), in the text is intended to merely illuminate the invention anddoes not pose a limitation on the scope of the same, unless otherwiseclaimed. Further, no language or wording in the specification should beconstrued as indicating any non-claimed element as essential to thepractice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be further described with referencesto the drawings, wherein

FIG. 1 is a perspective view of an exemplary injection device to which aneedle unit according to the present invention may be attached,

FIG. 2 is a longitudinal section view of a needle unit according to anembodiment of the invention,

FIG. 3 is a longitudinal section view of the needle unit with anattached drug cartridge,

FIG. 4 is a longitudinally sectioned perspective view of the needle unitand the drug cartridge in a first in-use state, during insertion of theinjection needle into the skin, and

FIG. 5 is a longitudinally sectioned perspective view of the needle unitand the drug cartridge in a second in-use state, during drug injection.

In the figures like structures are mainly identified by like referencenumerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

When in the following relative expressions, such as “upwards” and“downwards” and “left” and “right”, are used, these refer to theappended figures and not necessarily to an actual situation of use. Theshown figures are schematic representations for which reason theconfiguration of the different structures as well as their relativedimensions are intended to serve illustrative purposes only.

FIG. 1 is a perspective view of an exemplary injection pen 1 to which aneedle unit according to the present invention may be attached. Theinjection pen 1 has a longitudinal housing 2 which accommodates aninjection mechanism (not visible). A cartridge holder 3 is attached to adistal end portion of the housing 2 and supports a cartridge 60 holdinga liquid drug. At its own distal end the cartridge holder 3 is providedwith a needle mount 6 configured to receive and retain a needle unitcarrying an injection needle. The needle mount 6 comprises both a malethread 7 and a bayonet track 8, superposed onto the male thread 7, so asto be compatible with needle units having a thread interface as well asneedle units having a bayonet interface.

In the present case the cartridge holder 3 is fixedly attached to thehousing 2, as the injection pen 1 is of the so-called prefilledinjection device type. However, in other cases the cartridge holder 3could be detachably attached. In conventional fashion the injection pen1 has, arranged at a proximal end portion thereof, a dose dial button 4for selective setting of a dose to be delivered and an injection button5 for actuation of the injection mechanism, and a currently set dose canbe viewed through a window 9 in the housing 2. Non-exhaustive examplesof injection devices which may be used with a needle unit as presentedin the following are FlexTouch® and FlexPen®, manufactured by NovoNordisk A/S.

FIG. 2 is a longitudinal section view of a needle unit 10 according toan embodiment of the invention in a pre-use state. The needle unit 10has a base member 11 comprising an inner section 12 and an outer section13. A transversal partition 14 divides the inner section 12 to provide aproximal receiving space 15 and a distal receiving space 16. A portionof the inner section 12 in the proximal receiving space 15 carries afemale thread 17 for mating connection with the male thread 7 of theneedle mount 6. The needle unit 10 further comprises a needle hub 25,carrying an injection needle 20 which extends along a generallongitudinal axis, and a needle shield 50. The needle hub 25 is axiallyslidably arranged in the distal receiving space 16.

The injection needle 20 comprises an elongated needle tube 21 having alumen 24, a proximal needle end 22 which is configured for penetrationof a cartridge septum and residence in a cartridge interior, and adistal needle end 23 configured for insertion through the skin of theuser. The needle tube 21 is fixedly mounted in the needle hub 25.

The needle shield 50 comprises a circumferential side wall 58, atransversal end wall 51, having a contact surface 53 for abutment with askin portion surrounding the injection site and a central orifice 55,and an interior chamber structure 56 which carries an antibacterial plug38 of rubber. The antibacterial plug 38 has a free distal end which isexposed to the surroundings via the orifice 55.

A shield spring 40, in the form of a compression spring, is arranged toact between the base member 11 and the needle shield 50, and a hubspring 45, also in the form of a compression spring, is arranged to actbetween the base member 11 and the needle hub 25.

In the depicted pre-use state of the needle unit 10 a distal portion ofthe needle tube 21, including the distal needle end 23, resides withinthe antibacterial plug 38, having gained access thereto via a proximalopening in the chamber structure 56, and a proximal portion of theneedle tube 21, including the proximal needle end 22, resides within thereceiving space 15, having gained access thereto via a bore in thetransversal partition 14.

FIG. 3 shows the needle unit 10 in a situation where the proximalreceiving space 15 is occupied by a head portion of the cartridge 60 andthe needle mount 6 of the cartridge holder 3, the male thread 7 beingmated with the female thread 17. In this position of the cartridgeholder 3 the proximal needle end 22 has penetrated a self-sealingcartridge septum 61 at the distal end of the cartridge 60, and aproximal end portion of the needle tube 21 thus extends from thecartridge septum 61 into a cartridge interior 65, establishing fluidcommunication with a liquid drug 66 (ref. FIG. 5 ) therein.

The needle shield 50 and the needle hub 25 are capable of relative axialmotion between a needle covering relative position (shown in FIG. 3 ) inwhich the distal needle end 23 is accommodated within the antibacterialplug 38 and a needle exposing relative position (shown in FIG. 4 ) inwhich the distal needle end 23 protrudes from the antibacterial plug 38through the orifice 55. In the needle covering relative position adistal rim 26 of the needle hub 25 and an inner surface 52 of the endwall 51 are spaced apart a distance, X₁, which reflects the extent ofpossible relative axial motion between the needle shield 50 and theneedle hub 25.

Further, the needle shield 50 and the base member 11 are capable ofrelative axial motion between a fully extended relative position (shownin FIG. 3 ), in which the needle shield 50 and the needle hub 25 are inthe needle covering relative position, and a fully displaced relativeposition (shown in FIG. 5 ). The shield spring 40 biases the needleshield 50 and the needle hub 25 towards the fully extended relativeposition.

In the fully extended relative position a proximally facingcircumferential ledge 54 of the needle shield 50 and a distal face of anouter section protrusion 18 of the base member 11 are spaced apart adistance, X, which reflects the extent of possible relative axial motionbetween the needle shield 50 and the base member 11. Notably, X>X₁.

FIG. 4 is a longitudinally sectioned perspective view of the needle unit10 and the cartridge 60 during insertion of the injection needle 20 intothe skin (not shown). In the depicted state of the needle unit 10 theneedle shield 50 and the base member 11 are in an intermediate relativeposition between the fully extended relative position and the fullydisplaced relative position in which the distal rim 26 of the needle hub25 and the inner surface 52 of the end wall 51 have just been broughtinto contact, i.e. where the needle shield 50 and the needle hub 25 havebeen brought to the needle exposing relative position and where furtherconverging motion between the needle shield 50 and the needle hub 25 isprevented.

During the relative axial motion between the needle shield 50 and thebase member 11 that brings the two from the fully extended relativeposition to the intermediate position the outer section protrusion 18travels along a longitudinal shield track 57, and the distance betweenthe proximally facing circumferential ledge 54 and the distal face ofthe outer section protrusion 18 is thereby eventually reduced from X toX₂.

At this point the distal needle end 23 protrudes through the orifice 55in correspondence with the desired needle insertion depth. Nevertheless,the needle shield 50 and the base member 11 are capable of furtherrelative axial motion until the fully displaced relative position isreached. Also, the needle hub 25 and the base member 11 are capable ofrelative axial motion, against a biasing force from the hub spring 45.The extent of said motion is defined by the travel of an inner sectionprotrusion 19 of the base member 11 along a longitudinal hub track 27from a proximal hub track end (at which it is situated in FIG. 4 ) to adistal hub track end (at which it is situated in FIG. 5 ).

FIG. 5 shows the needle unit 10 and the cartridge 60 in a state wherethe needle shield 50 and the base member 11 are in the fully displacedrelative position and an injection of a dose of the liquid drug 66 hascommenced.

In summary, describing a situation of use where the needle unit 10 isalready mounted on the needle mount 6, when an injection is needed thecontact surface 53 is placed against a skin portion of the user and theinjection pen 1 is pressed towards the skin. This action causes arelative axial motion between the base member 11 and the needle shield50, which compresses the shield spring 50. Initially, the needle hub 25remains stationary relative to the base member 11, being biased distallyby the hub spring 45 while the inner section protrusion 19 at theproximal hub track end prevents distal motion of the needle hub 25relative to the inner section 12.

Hence, during the first part of the relative axial motion between thebase member 11 and the needle shield 50, which takes the base member 11and the needle shield 50 from the fully extended relative position tothe intermediate relative position, the needle shield 50 also undergoesrelative axial motion with respect to the needle hub 25, said relativeaxial motion bringing the needle shield 50 and the needle hub 25 fromthe needle covering relative position to the needle exposing relativeposition.

In the needle exposing relative position, the transversal end wall 51abuts the distal rim 26, and the distal needle end 23 protrudes throughthe orifice 55 a distance corresponding to the intended insertion depthin the skin. However, at this point the user cannot know if the distalneedle end 23 has actually reached the intended insertion depth, as theentire injection needle 20 is hidden from the user's eyesight behind thebase member 11, the needle shield 50, and the skin surface. The skinsurface may in fact have deformed undesirably to produce a cavity aroundthe orifice 55, such that only a portion of the distal needle end 23 haspenetrated the skin, or maybe even such that the distal needle end 23has not penetrated the skin at all. Obviously, this situation isunfortunate, as a proper injection treatment requires a properdeposition of the drug in the skin.

However, the particular construction of the needle unit 10 urges theuser to press the injection pen 1 further towards the skin in order toeliminate the visible gap, X₂, between the proximally facingcircumferential ledge 54 and the distal face of the outer sectionprotrusion 18, which gives the impression that the needle shield 50 isnot sufficiently depressed. This causes a further relative axial motionbetween the base member 11 and the needle shield 50 towards the fullydisplaced relative position, although now the needle shield 50 slavesthe needle hub 25 which then also undergoes relative axial motion withrespect to the base member 11.

Thus, the relative axial motion between the base member 11 and theneedle shield 50 from the intermediate relative position to the fullydisplaced relative position occurs against the force from the shieldspring 40 but also against the additional force from the hub spring 45,requiring an extra effort from the user. Notably, since the needleshield 50 and the needle hub 25 do not undergo any relative axial motionat this stage the position of the distal needle end 23 relative to thetransversal end wall 51 does not change. In other words, the needleshield 50 and the needle hub 25 remain in the needle exposing relativeposition as the base member 11 and the needle shield 50 undergo relativemotion from the intermediate relative position to the fully displacedrelative position. The proximal needle end 22, however, is moved furtherinto the cartridge interior 65 due to the needle hub 25 being displacedproximally in the distal receiving space 16.

The fact that the needle unit 10 comprises a spring loaded over-travelfeature for the needle shield 50, and that the user must apply a totalcompression force which exceeds the compression force needed to exposethe distal needle end 23 in order to seemingly obtain a sufficientdisplacement of the needle shield 50, ensures that the needle unit 10maintains full contact with the skin during the injection procedure,thereby eliminating the risk of skin pocket generation and providing fora proper insertion of the distal needle end 23.

When the inner section protrusion 19 reaches the distal hub track endfurther converging relative axial motion between the needle hub 25 andthe base member 11 is prevented, as is further converging relative axialmotion between the base member 11 and the needle shield 50. The basemember 11 and the needle shield 50 are now in the fully displacedrelative position, and the distal needle end 23 is properly positionedin the skin. The user can therefore operate the injection button 5 toinitiate the injection of the set dose well aware that the dose will beadministered to the intended body compartment.

After completed dose administration the user withdraws the injectionneedle 20 from the skin by simply pulling back the injection pen 1. Thehub spring 45 will thereby return the needle hub 25 to the positionwhere the inner section protrusion 19 abuts the proximal hub track end,and the shield spring 40 will ensure that the base member 11 and theneedle shield 50 return to the fully extended relative position. Thedistal needle end 23 is thereby returned to the interior chamberstructure 56 where it will reside within the antibacterial plug 38.

The antibacterial plug 38 will disinfect the distal needle end 23 afterthe injection such that the injection needle 20 may be safely reused forone or more subsequent injection(s). The needle unit 10 can thereforeremain on the injection pen 1, with the female thread 17 and the malethread 7 in interengagement, between injections, thus reducing thenumber of required needle handling actions.

1. A needle unit for use with a pen injection device, comprising: a basemember for attachment to a needle mount of the pen injection device, thebase member extending along a main axis and comprising an interiorattachment portion defining a proximal receiving space and beingconfigured for reception and retention of the needle mount, a needle hubcoupled with the base member distally of the interior attachmentportion, an injection needle fixedly mounted in the needle hub andcomprising a distal needle end portion intended for insertion through askin barrier, and a proximal needle end portion extending into theproximal receiving space and permanently residing therein, a needleshield arranged exteriorly of the needle hub and comprising an axiallyextending wall, the needle shield being axially displaceable relative tothe base member between an extended position and an intermediateposition and further between the intermediate position and a maximumdisplaced position, and a first bias structure biasing the needle shieldtowards the extended position, wherein the needle hub is axiallyreciprocatable relative to the base member between a proximal needle hubposition and a distal needle hub position, the needle hub being biasedtowards the distal needle hub position by a second bias structure whichacts between the base member and the needle hub, wherein during axialdisplacement from the extended position to the intermediate position theneedle shield undergoes relative motion with respect to the needle hubfrom a needle covering relative position in which the distal needle endportion is surrounded by the axially extending wall to a needle exposingrelative position in which the distal needle end portion extendsdistally beyond the axially extending wall, and wherein during axialdisplacement from the intermediate position to the maximum displacedposition the needle shield undergoes joint motion with the needle hubwhich brings the needle hub from the distal needle hub position to theproximal needle hub position.
 2. A needle unit according to claim 1,wherein the needle shield comprises an interior chamber structureholding an antibacterial substance, and wherein the distal needle endportion resides in the antibacterial substance when the needle shield isin the extended position.
 3. A needle unit according to claim 2, whereinthe antibacterial substance comprises an antibacterial rubber plug.
 4. Aneedle unit according to claim 2, wherein the antibacterial substancecomprises a preservative containing liquid drug.
 5. A needle unitaccording to claim 1, wherein the first bias structure comprises a firstcompression spring acting between the base member and the needle shield,and the second bias structure comprises a second compression spring. 6.A needle unit according to claim 1, wherein an exterior surface portionof the needle hub comprises a longitudinal hub track, and wherein thebase member further comprises an inner section carrying a radiallyinwardly directed inner section protrusion adapted to travel thelongitudinal hub track between a proximal hub track end and a distal hubtrack end, a position of the radially inwardly directed inner sectionprotrusion at the proximal hub track end defining the distal needle hubposition, and a position of the radially inwardly directed inner sectionprotrusion at the distal hub track end defining the proximal needle hubposition.
 7. A needle unit according to claim 1, wherein an exteriorsurface portion of the needle shield comprises a longitudinal shieldtrack, and wherein the base member further comprises an outer sectioncarrying a radially inwardly directed outer section protrusion adaptedto travel the longitudinal shield track between a proximal shield trackend and a distal shield track end, a position of the radially inwardlydirected outer section protrusion at the proximal shield track enddefining the extended position, and a position of the radially inwardlydirected outer section protrusion at the distal shield track enddefining the maximum displaced position.
 8. A needle unit according toclaim 6, wherein the interior attachment portion forms part of the innersection, and wherein the inner section further comprises a transversalpartition adjacent a distal end section of the interior attachmentportion, the transversal partition comprising a through-going bore forslidable reception of the injection needle.
 9. An injection systemcomprising the needle unit according to claim 1 and the pen injectiondevice comprising the needle mount, wherein the needle mount and theinterior attachment portion are configured for releasableinterengagement.
 10. An injection system comprising the needle unitaccording to claim 1 and the pen injection device comprising the needlemount, wherein the needle mount is permanently engaged with the interiorattachment portion.